The only hack I'd ever contemplate undertaking would be if you could hardwire TomTom navigation to appear on the display screen.
The nav system on my RX300 is from 2005 so the interface is a bit dated and as I've been a TomTom user since the early days, when you used a PDA and a separate GPS receiver, it is what I'm used to! The 3D view and lane indication are big advantages on more modern systems. I don't think this will ever happen due to integration issues with the other on screen functions.
It's not a big deal to attach my TomTom to the windscreen but it would be better if it were integrated!